The sister disease affects the pancreas and other organs, while leaving the lungs alone.
Thick mucus that can drown the lungs of a child has long been the hallmark of cystic fibrosis. The hereditary disease affects 30,000 Americans, and patients die unless they receive treatment to clear their lungs. But new research suggests that this pulmonary view of cystic fibrosis is only half of the picture: a suite of symptoms associated with cystic fibrosis can also occur in patients who do not have lung disease at all, indicating that cystic fibrosis is really two diseases. This second version, it appears, causes pancreatitis.
"Cystic fibrosis has been evaluated and managed by pulmonary doctors focusing on the lung, but other important problems are never seen by the pulmonologist and nobody's put the pieces together," says David Whitcomb of the University of Pittsburgh, who studies disorders of the pancreas.
Cystic fibrosis results from mutations in a gene that produces a tube-shaped protein known as CFTR, essential to the balance of electrolytes in the body. Specifically, this protein allows chloride ions to pass in and out of cells. When it malfunctions in classic cystic fibrosis, cells in the airway cannot produce normal mucus but instead make a thicker, stickier substance that clogs the lungs.
But CFTR leads a double life. Whitcomb's team screened a group of nearly 1,000 patients with pancreatitis and found nine abnormal but supposedly harmless versions of the CFTR gene. Their study suggests that the seemingly benign mutations break the switch that turns CFTR from a chloride portal to a channel for bicarbonate, a chemical that the pancreas produces to neutralize stomach acid. Patients with these mutations do not have the problems associated with the chloride channel, but the faulty bicarbonate channel means that they can suffer from painful pancreatitis, as well as sinusitis and, in men, infertility. Computer simulations confirmed that the mutations are all in places that would inhibit bicarbonate but not chloride from passing through.